Liquid crystal display device comprises a liquid crystal cell and at least one polarizing plate. The polarizing plate generally has protective films and a polarizing film, and is obtained typically by dying the polarizing film composed of a polyvinyl alcohol film with iodine, stretching, and being stacked on both surfaces thereof with the protective films. A transmissive liquid crystal display device is configured by attaching the polarizing plate on both sides of the liquid crystal cell, occasionally having one or more optical compensation film optionally arranged therein. A reflective liquid crystal display device is configured generally by arranging a reflector plate, the liquid crystal cell, one or more optical compensation films, and the polarizing plate in this order. The liquid crystal cell comprises liquid-crystalline molecules, two substrates encapsulating the liquid-crystalline molecules, and electrode layers applying voltage to the liquid-crystalline molecules. The liquid crystal cell switches ON and OFF displays depending on variation in orientation state of the liquid-crystalline molecules, and is applicable both to transmission type and reflective type. There are proposed several kinds of display modes including TN (twisted nematic), IPS (in-plane switching), OCB (optically compensatory bend) and VA (vertically aligned), ECB (electrically controlled birefringence).
Of these LCDs, most widely used for application in need of a high definition display is 90° twisted nematic liquid crystal display (referred to as “TN mode”, hereinafter) using nematic liquid crystal molecules having a positive dielectric anisotropy, driven by thin-film transistors. The TN mode has viewing angle characteristics such as ensuring an excellent display characteristic in the front view, but as being degraded in display characteristics in an oblique view, such as causing lowered contrast, or grayscale inversion which is inversion of brightness in gradation display, which are strongly desired to be improved. The TN mode also suffers from limitation of response speed, and this raises further need for development of LCD based on a liquid crystal mode capable of faster response.
The optical compensation film has conventionally been developed for use with TN-mode liquid crystal display device, but recent growing demands on liquid-crystal television set have raised newly-recognized problems of response speed which is observed as trailing or after-image in video image. OCB mode (or bend mode), characterized by a large response speed, has therefore attracted much attention. It is, however, difficult for the OCB mode to achieve a wide viewing angle characteristic, and this demands use of the optical compensation film. Japanese Laid-Open Patent Publication “Tokkaihei” Nos. 9-211444 and 11-316378, for example, describe the optical compensation film, having a layer composed of a liquid-crystalline compound, applicable to the liquid crystal display device based on the OCB system. It has, however, been difficult to obtain desirable viewing angle characteristics only by controlling the conventionally-known optical parameters described in these publications.